[Bug? or Help needed] with Unity 4.6 I have a Problem with Objectfields and a custom GUISkin

Hello, I'm developing an editor extension which makes use of a custom GUISkin and it worked everything well with Unity 4.5, until I started to use Unity 4.6...
I wanted to wait for the official 4.6 release to port my extension to it, so now that I tested it I don't get around the following problem:

When I display an Objectfield for texture selection (Objectfield stands under the EditorGUI Class not the normal GUI class), it asks me for an "ObjectFieldThumbOverlay" and "ObjectFieldThumbOverlay2" definition in the skin that I use. Now I have two questions:

Why does it need at all a ObjectFieldThumbOverlay in 4.6, when the Objectfield should be drawn from the native GUI Skin the Editor already has?

And if we really need to specify now a ObjectFieldThumbOverlay, where do we do that exactly?

I know how to do customstyles (indeed I use some in my own Skin and my extension, set everything up etc. and like I said it worked until 4.5), I can't find any way how to define it. The GUISkin Inspector in Unity only has options for Buttons, Textfields, Labels, Window etc. but none for Objectfields, and I guess defining the ObjectFieldThumbOverlay as a customstyle is not the solution, as the customstyles are accessed by an Array.. (like.: GUI.Skin.customStyles[2]). I even don't know how the ObjectFieldThumbOverlay should look like, any example available??

To see if I just did something wrong in my own code I quickly made this example as a test:

Code (CSharp):

1. using UnityEngine;
2. using UnityEditor;
3. using System.Collections;
4.  
5. namespace Valentactive.NewCompo
6. {
7.     public class NewCompo : EditorWindow
8.     {
9.  
10.         // Data:
11.         private Texture TextureToSet;
12.         private static GUISkin TagCompoSkin = null;
13.  
14.         // Adds menu entry named "NewCompo" to the Window menu
15.         // and initializes the variables:
16.         [MenuItem("Window/NewCompo")]
17.         static void Init()
18.         {
19.             NewCompo window = (NewCompo)EditorWindow.GetWindow(typeof(NewCompo));
20.             window.title = "Window1";
21.             if (TagCompoSkin == null)
22.             {
23.                 TagCompoSkin = (GUISkin)(Resources.LoadAssetAtPath("Assets/Editor/TagCompo/TagCompoSkin.guiskin", typeof(GUISkin)));
24.             }
25.        
26.         }
27.  
28.         void OnGUI()
29.         {
30.             GUI.skin = TagCompoSkin;  //Sets the skin to the "TagCompoSkin"
31.             EditorGUILayout.BeginVertical();
32.             EditorGUILayout.LabelField("Bug Example:");
33.             TextureToSet = (Texture)EditorGUILayout.ObjectField("Texture:", TextureToSet, typeof(Texture), false);  //Sets the private TextureToSet with the Texture that we chose on this Objectfield
34.             EditorGUILayout.EndVertical();
35.         }
36.     }
37. }
38.  

Or is it just a new bug?
Did anyone else face similar problems?